The present invention relates to a forced cooling apparatus for a heat treatment apparatus, for cooling a heater of a heat treatment apparatus used for example, in processes for the manufacture of semiconductor devices and the like.
The following is a description of a conventional example of a forced cooling apparatus for a heat treatment apparatus, used in processes for the manufacture of semiconductor devices and the like.
In such a heat treatment apparatus, heating semiconductor wafers by a required processing gas performs for example, the formation of an oxide film on the semiconductor wafer, thin film deposition by a thermal CVD method or the formation of high impurity concentration regions by a thermal diffusion method.
In addition, in such heat treatment apparatus, the temperature of the inside of the process tube is normally cooled to a required temperature after the heat treatment has been performed and then the semiconductor wafers are conveyed to outside of the furnace. When these high-temperature semiconductor wafers are carried to outside of the furnace, there is the formation of a natural oxidation film on the surface of the semiconductor wafers. This causes a reduction of the yield when semiconductor devices are manufactured from these semiconductor wafers, and also causes deterioration of the characteristics of the manufactured semiconductor wafers.
Also, with the recently increased requirements for higher integration and high speeds of integrated circuits, it is required that there be control for the depth of diffusion to semiconductor wafers. Controlling the depth of diffusion so that it is shallow requires that the semiconductor wafer which is the object of processing be raised to a required temperature in a short time and that the same program for the required temperature hold time and the temperature lowering time be reproduced for each processing.
Techniques for the uniform and fast performing of cooling inside a process tube of a heat treatment apparatus have been disclosed in Japanese Patent Laid-Open Publication (KOKAI) No. 121429-1988 and Japanese Patent Laid-Open Publication No. 8128-1988.
The apparatus disclosed in Japanese Patent Laid-Open Publication No. 121429-1988 performs cooling of the process tube by an spiral air flow formed along the outer periphery of a processing tube of a heat treatment apparatus.
In addition, the apparatus disclosed in Japanese Patent Laid-Open Publication No. 8128-1988 has the one opening of the furnace provided with either one or a plural number of air ejection pipes for the supply of cooled and compressed air between the process tube and the heater coil of the heat treating furnace, and is also provided with a plural number of air exhaust pipes for the exhaust of air from the furnace opening at the other end.
However, even with these conventional art, it was still not possible to have a sufficient uniformity of cooling and cooling speed for the process tube.
In addition, with the apparatus disclosed in Japanese Patent Laid-Open Publication No. 121429-1988, in actuality, it is extremely difficult to form a spiral-shaped air flow along the surface of the outer periphery of the process tube. In addition, even assuming that it was possible to form a spiral-shaped air flow along the surface of the outer periphery of the process tube through the provision of a means for guiding the flow of introduced air into a spiral shape, one still could not expect a sufficient cooling speed since there would be a large resistance to the flow of air.
On the other hand, with the apparatus disclosed in Japanese Patent Laid-Open Publication No. 8128-1988, pipes are used for the supply of the cooling air to the process tube, and also for its exhaust and so it is easy for the air flow to become uneven. There is also a limit to the degree of improvement of uniformity of cooling. Also, with this apparatus, the supply of the air for cooling is performed forcedly and its exhaust is also performed forcedly and so it is difficult to generate a uniform air flow around the periphery of the process tube.
Furthermore, this same problem exists with apparatus disclosed in Japanese Patent Laid-Open Publication No. 94626-1990 and Japanese Patent Laid-Open Publication No. 224217-1991.